The background description provided herein is for the purpose of generally presenting the context of the disclosure. Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Silicon photonics is often considered one of the most popular and successful technology platforms based on planar photonics circuits for cost effective optoelectronics integration. Optical waveguide-based photonics devices such as lasers, modulators, and detectors are typically fabricated on silicon-on-insulator (SOI) wafers. In SOI photonic systems, light is typically confined in a wafer (or chip) plane. Silicon waveguides are typically designed with submicron cross-sections, allowing dense integration of active and passive devices to achieve higher speed and lower driving power. Light transmitted from silicon SOI photonic systems is typically coupled off-chip in a non-vertical fashion. In some manufacturing scenarios, it is desirable to vertically couple light from silicon photonic transmitter chips to optical fibers in a direction orthogonal to the silicon photonic transmitter chip. However, orthogonal light emission from grating couplers, vertical in particular, typically has severely limited performance due to large back-reflection and/or losses resulting from higher order diffraction such that when grating couplers are used they have been restricted to non-orthogonal/non-vertical light emission that is typically greater than five to ten degrees from a vertical direction orthogonal to the chip to suppress higher order diffraction either along the return path or off-chip.